An optical disk drive may be subdivided into a host part, a servo part, and a mechanical part. The host part belongs to the top level and the servo part receives instructions from the host part to drive the mechanical part.
In order to obtain data from an optical disk medium, the host part assigns read addresses and the servo part drives the mechanical part. In general, the driving of the mechanical part includes driving an actuator, driving a spindle, and seeking. Properly actuating the mechanical part reads an analog signal from the optical disk medium.
The servo part slices the radio frequency(RF) signal read from the optical disk medium to a sliced signal, prepares data in a particular format, and transmits the prepared data to the host part. The host part performs demodulation and error correction based on the data to reproduce image and sound.
In the above steps, faults such as data errors, in particular, reproduction of broken images or reproduction of abnormal video, mainly stem from the mechanical part. The data error is frequently generated from a pickup head (PUH) in the mechanical part. The causes for the data errors generated from the pickup head are generally divided into unbalanced servo tracking and a defective optical disk.
First, the unbalanced servo tracking results from a tolerance differences between devices constituting the circuitry involved in the servo loop of an optical signal. That is, the circuitry includes devices such as resistors, capacitors, and amplifiers. Since proper values of the devices are within certain tolerances from one another, unbalanced servo tracking may result.
Second, the defective optical disk results from a defective stamper in a mastering process, a defective substrate in an injection step, or a defective recording layer, during the disk manufacturing process. A scratch made by an end user may make an optical disk defective. Due to the media defect, servo tracking cannot be adequately performed and reproduction of signals from the optical disk may no longer be possible.
Nevertheless, when an error occurs during decoding in a conventional optical disk drive, a servo system has no option but to wait for a given time period. After the given time passes, a partial image is displayed or a previous image frame is reproduced.